“ADP provided non-public, inaccurate and misleading information, claims, and arguments which were relied upon by ISS,” Ackman said in a regulatory filing made with the U.S. Securities and Exchange Commission.

“ISS accepted, and in its Report has publicly endorsed, certain misleading or incorrect factual assertions made by ADP management during its engagement with ISS,” Ackman said in the filing.

The filing came less than one week after ISS issued a report to guide institutional investors in next week’s proxy vote where Ackman hopes to win three seats on the human resources outsourcing company’s board. (Reporting by Svea Herbst-Bayliss; Editing by Andrew Hay)